1. Field of the Invention
The present invention relates to a recliner adjuster attached to, for example, an automobile seat for appropriately adjusting the inclination of a seat back with respect to a seat cushion.
2. Description of the Related Art
Conventional reclining seats are provided with a recliner adjuster interposed between a seat cushion and a seat back hingedly connected to the seat cushion. The recliner adjuster includes a first bracket fixed to one of the seat cushion and the seat back and a second bracket fixed to the other of the seat cushion and the seat back and mounted on the first bracket so that one of the first and second brackets can rotate relative to the other.
The recliner adjuster also includes a cam interposed between the first and second brackets and fixed to a support shaft that is concentrically aligned with a center of rotation of one of the first and second brackets relative to the other. Rotation of the support shaft rotates the cam, which in turn causes a lock plate to slide radially outwardly or inwardly between the first and second brackets. The first bracket has a radially extending guide groove having opposite parallel side walls. The lock plate has teeth formed on the outer periphery thereof and is slidably disposed within the guide groove.
On the other hand, the second bracket has internal teeth concentrically formed around the center of rotation referred to above. When the lock plate slides radially outwardly along the guide groove upon rotation of the cam together with the support shaft, the teeth of the lock plate are brought into engagement with the internal teeth of the second bracket, resulting in locking of the first and second brackets. Reverse rotation of the cam releases the engagement of the teeth of the lock plate with the internal teeth of the second bracket, thus allowing one of the first and second brackets to rotate relative to the other.
Accordingly, when an operating rod connected to the support shaft is operated, the teeth of the lock plate engage with the internal teeth of the second bracket to retain the inclination of the seat back, or the teeth of the lock plate disengage from the internal teeth of the second bracket so that the inclination of the seat back can be changed as desired (see, for example, Japanese Laid-Open Patent Publication No. 2000-342370).
Furthermore, another recliner adjuster has been proposed wherein a plurality of lock plates that are operable to slide in the radial direction by rotation of a cam are provided at predetermined intervals, and an auxiliary lock plate is interposed between two adjacent lock plates. According to this recliner adjuster, when a large load has been applied to the seat back, teeth of the auxiliary lock plate engage with internal teeth to withstand the large load that may be caused by, for example, a collision of an automotive vehicle (see, for example, Japanese Laid-Open Patent Publication No. 2000-245561).
In the conventional recliner adjuster as disclosed in Japanese Laid-Open Patent Publication No. 2000-342370, a large load applied to the seat back presses the lock plate against a side wall of the guide groove and occasionally causes deformation of the side wall, which in turn causes inclination of the lock plate and lowers the engagement between the teeth of the lock plate and the internal teeth, thus lowering the locking strength.
On the other hand, the recliner adjuster as disclosed in Japanese Laid-Open Patent Publication No. 2000-245561 includes a plurality of stoppers each interposed between one of the lock plates and one of the auxiliary lock plates adjacent thereto. The stoppers act to hold the auxiliary lock plates at respective predetermined positions under normal conditions and engage the auxiliary lock plates with the internal teeth when a large load has been inputted. Because this recliner adjuster is provided with a lot of movable members, the number of manufacturing or assembling processes increases and there is still a room for improvement in reliability.